This invention relates to thickened polyester resins and to techniques for making same.
In the art of making and using polyester resins, it has been generally desirable to produce a curable product comprised of unsaturated polyester resin and vinyl monomer which, for certain applications, is thickened relative to the condition of the polyester resin vinyl monomer composition in its freshly prepared or initial state. Such applications include, for examples, sheet molding compositions, laminating compositions, gel coating compositions, and, in general, compositions useful in polyester application situations, where it is desirable for the resin composition to be thickened prior to being cured. In particular, in the manufacture of sheet molding compositions, it is desirable to have a low viscosity liquid resin system initially so that many additives and compounds can be mixed with it, and then to have controlled thickening of the resin system up to a stage where it can then be molded by conventional sheet molding techniques and finally cured.
Heretofore, the art has taught that aluminum alkoxides and certain related organoaluminum compounds can be employed under certain circumstances in polyester/vinyl monomer systems to increase resin system viscosity and thixotropic characteristics (see, for example, Watanabe et al U.S. Pat. No. 3,361,845; Williger U.S. Pat. No. 3,536,642; Nikki German Auslegeshrift No. 1,164,089; and Asahi British Pat. Specification No. 1,092,528.) In this art, it has been previously theorized that the reaction of the aluminum alkoxides (and other organoaluminum compounds as disclosed in, for example, Bailey U.S. Pat. No. 4,049,748) with the terminal carboxyl and hydroxyl groups of the resin and with water (and perhaps other impurities present in the system) produces by-product alcohol which normally does not escape from the system of resin vinyl monomer and aluminum alkoxide prior to its being cured. The following is illustrative of three of the most likely reactions: ##STR1## where R' and R" represent resin molecules or hydrocarbon chains as impurities in the resin, R is a hydrocarbyl radical, and HOH represents trace amounts of water left in the resin from the esterification process. As can be seen by this illustration, the complete reaction of a trifunctional aluminum alkoxide produces 3 moles of alcohol (ROH) per mole of aluminum alkoxide as a by-product. In a like manner, a difunctional aluminum alkoxide produces 2 moles of alcohol per mole of aluminum alkoxide, and also a monofunctional aluminum alkoxide produces one mole of of alcohol per mole of aluminum alkoxide when such alkoxide is reacted with the polyester resin.
The presence of this by-product alcohol diminishes the improved chemical resistance effect in cured polyester resin systems generally attributed to aluminum alkoxides.
This alcohol in a polyester resin/vinyl monomer composition is essentially a non-reactive material which behaves as a diluent. Thus, when a curable composition of polyester resin and vinyl monomer which contains, for example, aluminum alkoxide is cured, the inherently produced by-product alcohol remains in the cured resin as a non-reactive diluent. Depending on the particular resin and aluminum derivative used, such alcohol in effect can be regarded as a hydrophilic agent which operates to reduce cured resin chemical resistance. In general, the presence of such a by-product alcohol has an adverse effect upon cured resin physical properties and chemical resistance.
It would be highly desirable, in order to overcome the problem of the inherent by-product alcohol production achieved through addition of aluminum alkoxide to a starting polyester resin vinyl monomer system, to be able to use instead of such prior art organoaluminum compound, a different organoaluminum compound which accomplishes a desired viscosity change (increase) without producing such a by-product alcohol. Further, it would be desirable to be able to use a different organoaluminum compound which reacts with a polyester resin and causes solely the effect of achieving increased cured resin moisture resistance and this at a concentration level which produces little or no thickening (viscosity increase) in uncured resin composition, all without having such a moisture resistance reducing by-product alcohol produced in such product resin compositions inherently.
My copending application U.S. Ser. No. 917,263 filed June 20, 1978 and now abandoned teaches that, when aluminum alkoxide is employed to thicken polyester resins, the moisture content of the resin must be adjusted to the approximate ratio of one mole of water per mole of aluminum alkoxide to achieve optimum thickening for a given amount of aluminum alkoxide. Since the trace amount of water inherently left in the resin from the esterification process varies from resin to resin, and even from one batch to another of the same resin, it is necessary in most cases to determine for each batch the exact amount of additional moisture needed by a given resin batch. Such above indicated copending application provides a technique for determining how much water is needed in a given batch to achieve maximum thickening with a given quantity of a specific organoaluminum compound of the class taught by Bailey U.S. Pat. No. 4,049,748. It would be highly desirable to be able to use a polyester resin reactive organoaluminum compound other than one of the types described in Bailey U.S. Pat. No. 4,049,748 for thickening a polyester resin/vinyl monomer composition which different compound would obviate the need for employing such water add technique. Eliminating the requirement for water adding would result in predicability and simplicity in polyester resin thickening using organoaluminum materials.
Organoaluminum compounds where a carbon atom of the organic moiety is connected to the aluminum atom through an oxygen linkage generally appear to be desirable for use in polyester/vinyl monomer systems except for these two deficiencies (by-product alcohol production and moisture determination steps) because such organoaluminum compounds generally have the useful characteristic of reactability with carboxyl groups and hydroxyl groups which groups are both commonly found as chain terminating moieties in polyester resins. Also, such organoaluminum compounds tend to be compatible with polyester resins without causing excessively adverse side reactions, storage problems, or the like. Further, such organoaluminum compounds are readily soluble both in the unsaturated polyester resins, as well as in the vinyl monomers characteristically employed therewith, in commerical polyester compositions.
The class of organoaluminum compounds known as aluminum acylates has previously been employed in alkyd gels to provide thixotropic paints or dripless paints (see Rinse U.S. Pat. No. 2,892,780). Although Example 6 of this patent uses the word polyester, it is obvious to those skilled in the art that this composition is in fact a coating resin which is clearly not the same type of polyester resin that is employed in molding applications.
In addition, if this coating polyester resin were to be dissolved in styrene as such Example 6 suggests, it would still produce a byproduct alcohol (isopropyl alcohol) which would be derived from the isopropyl radical in the hydroxyl isopropoxy aluminum stearate, and this byproduct alcohol would remain in the product resin as a nonreactive diluent, where it would interfere with physical properties and chemical resistance in a molded and cured product.
Rinse never appreciated that, or attached any significance to, the production of a byproduct alcohol as a result of organoaluminum compound addition to his alkyd gels. For one thing, the presence of a byproduct aluminum in an alkyd resin is of no particular detrimental effect upon such product material or compositions, e.g. paint compositions made thereof, for the reason that, once the coating is applied to a substrate as a layer and dried, the drying process permits a simple and effective means for removing the alcohol from such a layer or coating without producing a coating which has a structural weakness caused by the presence of the original alcohol during the curing thereof. In molding resins of the polyester type, however, a different situation prevails. Here it is not possible to effectuate the removal of the byproduct alcohol during curing to an extent sufficient to avoid a structural weakening of the final cured product compared to the same product in its cured state as it would exist without any of the byproduct alcohol being present therein.
For another thing, although Rinse in such U.S. Pat. No. 2,892,780 includes the possibility of aluminum acylate compounds of the form: ##STR2## wherein R is an organic moiety as defined by Rinse in such patent, Rinse nevertheless provides no teachings or exemplary information which would enable one skilled in the art to use such compounds in alkyd gels of the particular type disclosed by Rinse. The only example using aluminum acylates of this form is example 5 where an oxyaluminum stearate is added to an alkyd resin which in turn is added to a lubricating; oil to form a grease.
Moreover, there are no teachings in Rinse with regard to the properties of an alkyd resin made with such a structure as shown above (see formulas with the exception of the one used to make lubricating grease. In other words, Rinse never made either an alkyd coating resin or a polyester resin which had been treated with an organoaluminum compound of the class employed in the present invention (as hereinafter explained) which would inherently contain no alcohol byproduct resulting from a reaction of organoaluminum compound with polyester resin.
Rinse only discusses the thixotropic character of alkyd resins treated with the organoaluminum compounds identified by him (see column 1, lines 41 through 50 wherein the Rinse organoaluminum compounds are defined). In the case of unsaturated polyester molding resins, the control of viscosity and the achievement of a viscosity increase in a resin composition which contains vinyl monomer compared to the viscosity of a starting or freshly made such resin composition has substantial significance in terms of the ability of a resin composition user to employ that resin composition in various conventional end use applications, including spraying, lay-ups, sheet forming, and the like. In contrast, typically in the field of alkyd resins, such a relatively minor increase in viscosity is not as important as is the need to control thixotropic behavior. The thixotropic behavior of alkyds cannot properly be compared to, and is not equivalent to, the viscosity behavior in a polyester resin/vinyl monomer composition which has been treated with aluminum acylates utilized in the practice of the present invention.